* As steady as a clock: This emphasizes the reliability and consistent nature of a clock.
* Like a ticking bomb: This simile suggests a sense of urgency and impending danger.
* As precise as a clockwork mechanism: This highlights the intricate and accurate workings of a clock.
* Like a metronome, keeping time: This emphasizes the rhythmic and regular nature of a clock's ticking.
* As silent as a sundial: This compares a clock to a sundial, emphasizing its quiet operation.
The best simile for you will depend on the specific context and meaning you want to convey.